Polyacetal resins and thermoplastic aromatic polyesters, particularly polybutylene terephthalate resins have been used widely in various industrial fields including automotive, electric and electronic industries, as engineering plastics having excellent mechanical properties and chemical resistance in common use. Particularly, these resins have high frictional wear properties so that they are frequently used for electric and electronic apparatus parts, for example, machinery parts such as gears and cams or sliding part materials for connector and switch parts.
However, with the miniaturization and high performance development of electric and electronic apparatuses, the performance required for machinery parts in use is progressed and the properties that conventional resins possess only have been being insufficient for frictional wear properties.
Conventionally, a method of applying or immersing grease as an improver for sliding properties on molded article surfaces has been employed, but has a problem in that grease oozed on the molded article surfaces makes the surrounding parts dirty and the durability of effecting thereof as an improver for sliding properties is not sufficient.
Separately from this method, there has been a method of adding fluorine resins or a synthetic oil such as silicon oil or olefin polymerized oil as an additive to resin compositions for molding. The use of the compositions improves sliding properties of molded articles. However, it has a problem in that the fluorine resins are generally expensive, and these additives have inferior compatibility with polyacetal resins or thermoplastic aromatic polyester resins, thereby easily causing phase separation, or causing wetting or peeling on the molded article surfaces, and further, the releasability from molds is low at the molding, thereby causing mold contamination.
Therefore, the present applicant proposes in JP-A-11-5912/1999 a resin composition for molding prepared by adding a specific liquid oxidation modified ethylene/α-olefin random copolymer to polyacetal resins, ABS resins or thermoplastic polyester resins. Further, the present applicant proposes in JP-A-5-5912/1999 a resin composition for molding prepared by adding a liquid oxidation modified ethylene/α-olefin random copolymer to polyacetal resins, ABS resins or thermoplastic polyester resins. Furthermore, the present applicant proposes in JP-A-11-71439/1999 a resin composition for molding prepared by adding a graft modified copolymer obtainable by graft polymerization of a carboxylic acid monomer and/or a hydroxy group-containing ethylene unsaturated monomer on an ethylene/α-olefin random copolymer, to polyacetal resins, ABS resins or thermoplastic polyester resins.
The use of the resin composition for molding can lead molded articles having improved sliding properties and further those having low mold contamination, excellent moldability and excellent frictional wear properties. However, the more improvement of mechanical strength such as impact resistance or the like has been desired.
It is an object of the invention to provide resin compositions having low mold contamination, excellent moldability, excellent frictional wear properties, and favorable impact resistance to solve the above problems by improving compatibility between the polyacetal resins or thermoplastic aromatic polyester resins and the liquid ethylene/α-olefin random copolymers used as a lubricating oil.